DNA replication, transcription, repair, epigenetic inheritance, and chromosome segregation are all processes critical for maintaining cellular viability. In eukaryotes, these functions must be carried out on DNA that is organized into highly condensed chromatin. With the identification of an increasing number of disease-associated genes, the importance of chromatin in human disorders has become abundantly clear, and several diseases have been linked to defects in chromatin biology. To help understand how different aspects of DNA metabolism are influenced by chromatin we have developed unique technologies that allow us to directly visualize hundreds of individual DNA molecules at the single molecule level using optical microscopy. Here we will assess how nucleosomes influence the spatial and temporal progression of reactions related to DNA metabolism by visualizing these processes in real time using single molecule optical microscopy. We will analyze factors that influence nucleosome positioning, we will determine how nucleosomes affect DNA repair proteins, we will ask how nucleosomes are affected by interactions with DNA motor proteins, and we will begin working towards a mechanistic understanding of epigenetic phenomena. We will seek to determine detailed mechanistic information related to these questions, and part of the significance of this project lies in the depth of the answers we strive to obtain.